Apparatus for contacting a gas stream with a bed of particulate solids has utility in a variety of chemical engineering operations, including filtering of solids suspended in the gas, cooling or heating the gas or the solids, adsorption or absorption of constituents of the gas by the solids, or removal of constituents of the solids by the gas or removal of constituents of the gas by the solids through chemical reaction between the two. Currently there is considerable interest in continuously operating gas/solids contactors in which a gas stream passes through a bed of particulate solids moving downwardly through a vertically-elongated, tower-like structure, the gas and the solids being discharged separately for further treatment or for disposal. For example, in the case of cleaning a gas stream by removing fine particulate matter therefrom, the gas containing the fine particles is passed through a downwardly moving bed of solid filter granules, such as gravel or ceramic granules, on which the fine particles are deposited and retained. The granules are discharged from the lower end of the apparatus separately from the cleaned gas and can be regenerated by washing and recycled to the upper portion of the apparatus.
The present invention is directed to an improved gas/solids contactor for carrying out any of the many chemical engineering operations referred to above. The invention has special utility in removing sulfur oxides and nitrogen oxides from fossil fuel flue gas by reaction between these oxide constituents of the flue gas and a solid sorbent in the form of a bed of appropriate sorbent particles moving downwardly through the tower.
In each of the several embodiments described hereinafter the interior of the tower-like vessel is divided by internal wall structures into three axially-extending, concentric spaces. An inner space, typically of circular cross section and extending along the axis of the tower, receives the gas which is to be contacted with the particulate solids. An intermediate space, typically of annular configuration surrounds the inner space and, during operation of the contactor, contains the downwardly moving bed of particulate solids. An outer space, typically annular in configuration, surrounds the intermediate space and serves to collect gas which flows from the inner space, through the bed of particulate solids and into said outer space, appropriate passageways through the internal wall structure being present to permit such gas flow. The gas in the outer space flows out of the contactor through a suitable discharge pipe, and the particulate solids are discharged from the lower end of the vessel.
The present invention is directed primarily to the internal structure of contactors of the kind referred to in the previous paragraph, such internal structure providing improved gas/solids contact while maintaining a low gas pressure drop across the contactor and maintaining controlled flow of solids through the contactor.